The overall aim of the proposed research is to understand PKC-e and PKC-S function in the mammalian heart, with an emphasis on how these calcium-independent diacylglycerol-activated serine/threonine kinases regulate calcium handling and contractile properties. The overall hypothesis to be tested is that PKC-e and PKC-S can inhibit or stimulate cardiac contractility and calcium fluxes depending upon the subcellular compartments in which they accumulate. In Aim 1, native constructs of PKC-e and PKC-S isoforms will be fused with fluorescent proteins and expressed in adult rat ventricular myocytes to establish a link between PKC isoform expression level, sites of translocation, altered systolic calcium and inotropic responses. In Aim 2, use of dominant negative PKC-e and PKC-S constructs will address the isoform(s) involved in contractile responses to cell-permeable PKC activators and to agonists of G-protein coupled receptors. In Aim 3, the subcellular localization of diacylglycerol will be controlled independently of agonist receptors with light-activated caged compounds to determine diacylglycerol's functional effects in surface membranes, transverse-tubules and perinuclear regions of adult rat myocytes. The outcome of this research will shed new light on mechanisms of action of PKC-e and PKC-S and their control by agonists such as the endothelin peptides and other agonists operating through G-protein coupled receptors. The endothelin/diacylglycerol/protein kinase C signaling system represents an important regulatory axis in the mammalian heart which is thought to play a central role in control of contractility, intracellular calcium, gene expression, growth, cell death, and the heart's response to chronic stress such as hypoxia/ischemia or high blood pressure. Evidence is also accumulating that this signaling system is altered in failing hearts and may contribute to disease progression. A better understanding of coupling between receptors and PKC isoforms, and the subcellluar compartments in which each isoform acts to regulate basic cardiac function, will ultimately provide a foundation on which to explore signaling defects and other mechanisms of cardiac dysfunction in various forms of heart disease.